Alkylation of organic aromatic compounds

ABSTRACT

Aromatic compounds are alkylated in a catalytic distillation, wherein the catalyst structure also serves as a distillation component by contacting the aromatic compound with a C 2  to C 10  olefin in the catalyst bed under 0.25 to 50 atmospheres of pressure and at temperatures in the range of 80° C. to 500° C., using as the catalyst a mole sieve characterized as acidic or an acidic cation exchange resin. For example, ethyl benzene is produced by feeding ethylene to about the mid point of the catalyst bed while benzene is conveniently added through the reflux in molar excess to that required to react with ethylene, thereby reacting substantially all of the ethylene and recovering benzene as the principal overhead and ethyl benzene in the bottoms.

This invention was made with Government support under DE-FC07-80CS40454awarded by the Department Of Energy. The Government has certain rightsin this invention.

This application is a continuation, of application Ser. No. 122,485,filed Nov. 15, 1987 and now abandoned, which is a continuation ofapplication Ser. No. 846,357 filed Mar. 31, 1986, now abandoned.

BACKGROUND OF THE INVENTION

1. Field Of The Invention

The present invention relates to a process for the alkylation of organicaromatic compounds. More particularly the invention relates to a processfor the concurrent alkylation and distillation of reaction components(reactants and products) in a catalyst bed wherein the catalyst alsoserves as the distillation structure.

2. Related Art

Recently a new method of carrying out catalytic reactions has beendeveloped,, wherein the components of the reaction system areconcurrently separable by distillation, using the catalyst structures asthe distillation structures. Such systems are described variously inU.S. Pat. Nos. 4,215,011; 4,232,530; 4,242,530; 4,250,052; 4,302,356;and 4,307,254 commonly assigned herewith. Briefly, a structure describedthere is a cloth belt with a plurality of pockets spaced along the belt,which is then wound in a helix about a spacing material such asstainless steel knitted mesh. These units are then disposed in thedistillation column reactor.

In addition, commonly assigned U.S. patent application, Ser. No. 307,120filed Sep. 30, 1981, discloses a variety of catalyst structures for thisuse and is incorporated herein.

Ethylbenzene and cumene are currently produced by the reaction ofbenzene and the respective olefin, i.e., ethylene and propylene by acidcatalysis. In some known processes the catalyst is highly corrosive andhas a relatively short life, e.g., AlCl₃, H₃ PO₄ on clay, BF₃ onalumina, and others require periodic regeneration, e.g., molecularsieves. The exothermicity of the reaction and the tendency to producepolysubstituted benzene require low benzene conversions per pass withlarge volume recycle in conventional processes. Advantages of thepresent invention are that the catalysts are not highly corrosive and donot require periodic regeneration, the heat of reaction is usedefficiently, only low volume is required and the the feed ratios canapproach unity.

SUMMARY OF THE INVENTION

Briefly, the present invention is a process for the alkylation oforganic aromatic compounds by contacting the organic aromatic compoundand a C₂ to C₂₀ olefin in a distillation column reactor containing afixed bed acidic catalytic distillation structure in a distillationreaction zone thereby catalytically reacting said organic aromaticcompound and said olefin to produce an alkylated organic aromaticproduct and concurrently in said fixed bed fractionating the resultantalkylated organic product from the unreacted materials. The catalyticdistillation structure provides both the catalytic sites and thedistillation sites. The alkylated organic aromatic product is withdrawnfrom the distillation column reactor at a point below the fixed bed andunreacted organic aromatic compound may be taken off as an overhead.Suitable acidic catalysts include molecular sieves (mole sieves) andcation exchange resins.

More specifically the mole sieve or cation exchange resin catalystpacking is of such a nature as to allow vapor flow through the bed, yetprovide a sufficient surface area for catalytic contact as described inthe previously noted U.S. application Ser. No. 307,120 filed Sep. 30,1981, and U.S. Pat. Nos. 4,215,011 and 4,302,356 which are incorporatedherein in their entirety. The catalyst packing is preferably arranged inthe upper portion of the distillation column reactor, more preferablyoccupying about one-third to one-half of the column and extendingsubstantially to the upper end thereof.

The olefin feed to the reaction is preferably made into the catalyst bedthereby allowing immediate contact of this reactant with the organicaromatic compound in the catalyst to thereby react as much of the two aspossible and reduce or eliminate the olefin leaving the reactor asoverhead or bottoms. The exact location of the olefin feed will dependon the particular feeds and the desired product, but generally the feedwill be between the bottom of the fixed bed and the upper one-fourthsection thereof preferably in the middle one-half of the bed. Thecatalyst bed may be split at the point of olefin feed for the purpose ofdispersion. For example, in the case of alkylation of benzene (B.P. 80°C.), the olefin feed may be located at the mid point or lower portion ofthe bed preferably in the middle one-half of the bed, whereas,alkylation of benzene with decene (B.P. 170° C.) the decene ispreferably fed into the upper half of the bed.

The organic aromatic compound feed may be added at any point in thereactor, however, preferably it is added to the fixed bed or to thereflux as makeup.

Also, in order to achieve high selectivity toward monosubstitution(which is a preferred aspect of the present invention), there is a largeexcess of the organic aromatic compound to the olefin in the reactor inthe range of 2 to 100 moles of organic aromatic compounds per mole ofolefin, that is the net molar feed ratio of aromatic organiccompound:olefin may be close to 1:1, although the system is operated soas to maintain a substantial molar excess of organic aromatic compoundto olefin in the reaction zone.

The alkylated product is the highest boiling material and is separatedin the lower portion of the column usually as bottoms. The organicaromatic compound can be the second highest boiling or third highestboiling component (excluding inerts) as noted above, however, byoperating with a large excess of the organic aromatic compound, themajor portion of the olefin is reacted, thereby reducing the separationand recovery problems. The success of catalytic distillation lies in anunderstanding of the principles associated with distillation. First,because the reaction is occurring concurrently with distillation, theinitial reaction product is removed from the reaction zone as quickly asit is formed. The removal of the alkylation product minimizespolysubstitution, decomposition of the alkylation product and/oroligomerization of the olefin. Second, because the organic aromaticcompound is boiling, the temperature of the reaction is controlled bythe boiling point of that components at the system pressure. The heat ofthe reaction simply creates more boil up, but no increase intemperature. Third, the reaction has an increased driving force becausethe reaction products have been removed and cannot contribute to areverse reaction (Le Chatelier's Principle).

As a result, a great deal of control over the rate of reaction anddistribution of products can be achieved by regulating the systempressure. Also, adjusting the through-put (residence time=liquid hourlyspace velocity⁻¹) gives further control of product distribution anddegree of olefin conversion.

The temperature in the reactor is determined by the boiling point of theliquid mixture present at any given pressure. The temperature in thelower portions of the column will reflect the constitution of thematerial in that part of the column, which will be higher than theoverhead; that is, at constant pressure a change in the temperature ofthe system indicates a change in the composition in the column. Tochange the temperature the pressure is changed. Temperature control inthe reaction zone is thus controlled by the pressure; by increasing thepressure, the temperature in the system is increased, and vice versa.

It can also be appreciated that in catalytic distillation as in anydistillation there is both a liquid phase (internal reflux) and a vaporphase. Thus, the reactants are partially in liquid phase which allowsfor a more dense concentration of molecules for reaction, whereas, theconcurrent fractionation separates product and unreacted materials,providing the benefits of a liquid phase system (and a vapor phasesystem) while avoiding the detriment of having all of the components ofthe reaction system continually in contact with the catalyst which wouldlimit the conversion to the equilibrium of the reaction systemcomponents.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is a schematic representation of a preferred embodiment ofone species of the present invention for producing ethyl benzene.

DETAILED DESCRIPTION OF THE INVENTION

The olefins may be C₂ to C₂₀ olefins, preferably C₂ to C₁₂ olefins,including normal and branched forms thereof. For example, suitableolefins are ethylene, propylene, butylene, isobutylene, 1-pentene,1-hexene, 2-hexene, 2, 3-dimethyl-1-pentene, 1-octene, diisobutylene,1-nonene and 1-decene, dodecene and the like. The olefins may containsubstituents which do not interfere with the alkylation, much as halogenor hydroxyl radicals, e.g., vinyl chloride, 2-chloro-1-octene, 2-bromopentene-1, 1-pentene-3-ol, 4-methyl-1-heptene-4-ol and the like. In onepreferred embodiment the olefin is a C₂ to C₄ olefin.

In some reactions according to the present invention, the olefin will bea higher boiling material than the organic aromatic compound, e.g., C₈to C₂₀ olefins. In such instances any unreacted olefin will appear inthe bottoms alkylation product, although a side draw may be used toreduce such material in the product to an insignificant level. However,operating the reaction with far less than a stoichiometric amount ofolefin in the reaction zone, as described, will normally keep the olefinlevel in the bottoms low or entirely eliminated.

In those instances wherein the olefin is lower boiling than the organicaromatic compound, e.g., C₂ to C₇, there may be some olefin goingoverhead even with the large molar excess of the organic aromaticcompound present in the reaction zone. In those instances the overheadmay be condensed to remove a major portion of the organic aromaticcompound and the olefin and inerts removed for further separation oruse.

Similarly inerts such as the alkane of the particular olefin(s) whichare often found in olefin streams will be a possible contaminantdepending on its boiling point in either the bottoms or overhead.

The organic aromatic compounds are preferably those having a boilingpoint of 250° C. or less under the pressure conditions of thedistillation column reactor. The organic aromatic compounds includehydrocarbons of one or more rings and 6 to 20 carbon atoms which maycontain substituents which do not interfere with the alkylationincluding halogen (Cl, Br, F and I), OH and alkyl, cycloalkyl, aralkyland alkaryl radicals of 1 to 10 carbon atoms. Suitable organic aromaticcompounds include benzene, xylene, toluene, phenol, cresol, ethylbenzene, diethyl benzene, naphthalene, indene, phenyl bromide,1-bromo-2-chloro-benzene, 1-bromo-4-cyclohexyl benzene,2-bromo-1,4-dihydroxy-benzene, 1(bromo-methyl) naphthalene,1,2-dihydronaphthalene and the like. A preferred group of compounds foruse in the present process is benzene, xylene, toluene, phenol, andcresol.

The mole ratio of organic aromatic compound to olefin may be in therange of 2 to 100:1, preferably 2 to 50:1 and more desirably about 2 to10:1. The greater the excess of organic aromatic compound the more theselectivity to the monosubstituted product is improved. Alkylation isforced to completion, since the simultaneous and concurrentfractionation and removal of the alkylation product from thedistillation column reactor does not allow the products to contribute tothe reverse reaction (Le Chatelier's Principle). However, very largemolar excesses of organic aromatic compounds require a very high refluxratio, and a low unit productivity. Hence, the correct ratio of organicaromatic compound to olefin must be determined for each combination ofreactants as well as the acceptable olefin content in either theoverhead or alkylation product (as described above).

In a particular embodiment which is of current commercial importanceethylene or propylene is reacted with benzene according to the presentinvention to form ethyl benzene or cumene, respectively. In both ofthese reactions the olefin is the most volatile component and it isdesirable to react it rather than have some carried off overhead. Thepresence of ethylene, propylene or other lower boiling olefin in thetower with benzene will result in a small but detectable temperaturedepression in the tower where such lower boiling olefins are present asentities and unreacted. As the ethylene, propylene or other lowerboiling olefin is reacted with benzene, the depressing effect isdiminished and, furthermore, the reaction, which is exothermic alsodiminishes the effect. The magnitude of the temperature depressionimmediately above the olefin feed is a measure of the concentration ofethylene or other lower boiling olefin in the system, that is, thelarger the concentration of the lower boiling olefin, the greater thedepression of the temperature where the benzene and olefin are initiallytogether and yet unreacted. For any particular system the concentrationof the olefin to provide a given temperature depression can bedetermined and plotted. Thus, by maintaining a specific temperature atpoint of maximum temperature depression by adjusting the olefin feed, agiven ratio of olefin to benzene can be maintained in a simple andexpedient manner. More significantly, the maintenance of the depressionat a given temperature can assure that substantially all of the olefinwill be reacted prior to the end of the catalyst bed and overhead exit,if the corresponding olefin concentration has been determined to producethat effect.

This same control system can be employed in regard to any combination oflower boiling olefin and higher boiling organic aromatic compound.

The length of the catalyst bed, particularly that portion wherein thereactants are in contact and the major portion of the reaction occurs,depends on the reactants, location of the olefin feed and the acceptableunreacted olefin in the streams leaving the tower. Some degree ofdevelopment testing will be required for each set of reactants andparameters of stream purity following present disclosures.

The present alkylation reaction can be carried out at sub-through superatmospheric pressure, e.g., 0.20 to 40 atmospheres. The temperature willvary depending on the reactants and product. Furthermore, thetemperature along the column will be as in any distillation column, thehighest temperature will be in the bottom and the temperature along thecolumn will be the boiling point of the compositions at that point inthe column under the particular conditions of pressure. Moreover, theexothermic heat of reaction does not change the temperature in thecolumn, but merely causes more boil up. However, the temperatures withinthe column with the above considerations in mind will generally be inthe range of 70° C. to 500° C. for the mole sieve and 70° C. to 200° C.for the cation exchange resin, and more preferably in the range of about80° C. to 300° C. at pressures of 0.5 to 20 atmospheres for the molesieve and about 80° C. to 150° C. at 0.25 to 10 atmospheres for theresin catalyst.

Molecular sieves are porous crystalline, three-dimensionalalumina-silicates of the zeolite mineral group. The crystal skeleton iscomposed of silicon and aluminum atoms each surrounded by four oxygenatoms to form a small pyramid or tetrahedron (tetrahedral coordination).The term molecular sieve can be applied to both naturally occurringzeolites and synthetic zeolites. Naturally occurring zeolites haveirregular pore size and are not generally considered as equivalent tosynthetic zeolites. In the present invention, however, naturallyoccurring zeolites are acceptable so long as they are substantiallypure. The balance of the present discussion shall be directed to thesynthetic zeolites with the understanding that natural zeolites areconsidered equivalent thereto as indicated above, i.e. in so far as thenatural zeolites are the functional equivalents to the syntheticzeolites.

Usually synthetic zeolites are prepared in the sodium form, that is,with a sodium cation in close proximity to each aluminum tetrahedron andbalancing its charge. To date four principal types of molecular sieveshave been reported, A, X, Y and L. The A type have relative small poresize. By the term pore size is meant the effective pore size (diameter)rather than the free pore size (diameter). Types X and Y have largerpore size (approximately 10 A.) and differ as to the range of ratio ofAl₂ O₃ to SiO₂ as:

    ______________________________________                                        Type X            Al.sub.2 O.sub.3 /2.0-3.0 SiO.sub.2                         Type Y            Al.sub.2 O.sub.3 /3.0-6.0 SiO.sub.2                         Type L has still higher ratios of SiO.sub.2 to Al.sub.2 O.sub.3               ______________________________________                                    

The mole sieve catalysts employed in the present invention are the acidform mole sieves or exhibit acidic characteristics. The acid form of themole sieves is commercially available, but also may be prepared bytreating the mole sieves with acid to exchange Na for hydrogen. Anothermethod to produce the acid form is to treat the mole sieve withdecomposable cations (generally ammonium ions) to replace Na with thedecomposable ions and thereafter to heat the mole sieve to decompose thecation leaving the acid form. Generally the Na form mole sieve istreated with ammonium hydroxide to remove the Na and thereafter the molesieve is heated to a temperature of about 350° C. to remove the ammonia.The removal of Na⁺ ions with NH⁺ ₄ is more easily carried out than withmultivalent ions as described below and these catalysts are generallymore active, but less stable to heat than the multivalent cationexchange forms. Mole sieves, which have had their alkali metal reducedto low levels by partial treatment with NH⁺ ₄ and partial multivalentmetal cation exchange, possess increased activity and increasedstability.

In addition to mole sieves which are acidic according to the BronstedTheory, those mole sieves which exhibit acidic characteristics under theLewis Theory, for example, calcium exchanged mole sieves are suitablefor the present reaction. By exchanging the univalent cations (e.g. Na⁺)with multivalent cation, strong ionic activity is imparted. The ratio ofSiO₂ :Al₂ O₃, valence and radius of the cation and the extent ofexchange all affect the catalyst activity. In general activity increaseswith (1) increased SiO₂ :Al₂ O₃ ratio, (2) decreased cation radius andan increase in cation valence. The effect of replacing univalent ions(e.g. Na⁺) with bivalent (e.g. Ca⁺⁺) is much greater than replacing thebivalent ions with cations of greater valence.

The various types of mole sieves having reduced alkali metal content arecharacterized as the acid form molecular sieve and are all contemplatedas useful in the present invention.

It would appear that the pore size within the crystal lattice is notimportant to the present reaction. According to one theory of molecularsieve catalytic activity, zeolite catalysis occurs primarily inside theuniform crystal cavities, consequently zeolitic catalyst activitydepends on the number of aluminum atoms in the crystal and thus on thechemical composition of the crystal. Moreover, these catalytic sites arefixed within the rigid structure of the crystal, so that access to sitecan be altered by altering the structure of the crystal.

The acid form mole sieves are generally produced and available asparticles in the range of <10 micron (powders) to 0.2 inch in diameter(beads).

In this form the mole sieves form too compact a bed and will notfunction adequately in a distillation, since there is a very largepressure drop through the bed and the free flow of internal reflux andrising vapor is impeded. Mole sieves in the shape of conventionaldistillation structures, such as rings, saddles, and the like may beused in the present invention. The particulate mole sieves may beemployed by enclosing them in a porous container such as cloth, screenwire or polymeric mesh. The material used to make the container must beinert to the reactants and conditions in the reaction system. The clothmay be any material which meets this requirement such as cotton, fiberglass, polyester, nylon and the like. The screen wire may be aluminum,steel, stainless steel and the like. The polymer mesh may be nylon,teflon or the like. The mesh or threads per inch of the material used tomake the container is such that the catalyst is retained therein andwill not pass through the openings in the material. Particles of about0.15 mm size or powders may be used and particles up to about 1/4 inchdiameter may be employed in the containers.

Suitable acid cation exchange resins include those which containsulfonic acid groups, and which may be obtained by polymerization orcopolymerization of aromatic vinyl compounds followed by sulfonation.Examples of aromatic vinyl compounds suitable for preparing polymers orcopolymers are: styrene, vinyl toluene, vinyl naphthalene, vinylethylbenzene, methyl styrene , vinyl chlorobenzene and vinyl xylene. Alarge variety of methods may be used for preparing these polymers; forexample, polymerization alone or in admixture with other monovinylcompounds, or by crosslinking with polyvinyl compounds; for example,with divinyl benzene, divinyl toluene, divinylphenylether and others.The polymers may be prepared in the presence or absence of solvents ordispersing agents, and various polymerization initiators may be used,e.g., inorganic or organic peroxides, persulfates, etc.

The sulfonic acid group may be introduced into these vinyl aromaticpolymers by various known methods; for example, by sulfating thepolymers with concentrated sulfuric and chlorosulfonic acid, or bycopolymerizing aromatic compounds which contain sulfonic acid groups(see e.g., U.S. Pat. No. 2,366,007). Further sulfonic acid groups may beintroduced into the polymers which already contain sulfonic acid groups;for example, by treatment with fuming sulfuric acid, i.e., sulfuric acidwhich contains sulfur trioxide. The treatment with fuming sulfuric acidis preferably carried out at 0 to 150 degrees C. and the sulfuric acidshould contain sufficient sulfur trioxide so that it still contains 10to 50% free sulfur trioxide after the reaction. The resulting productspreferably contain an average of 1.3 to 1.8 sulfonic acid groups peraromatic nucleus. Particularly, suitable polymers which contain sulfonicacid groups are copolymers of aromatic monovinyl compounds with aromaticpolyvinyl compounds, particularly, divinyl compounds, in which thepolyvinyl benzene content is preferably 1 to 20% by weight of thecopolymer (see, for example, German Patent Specification 908,247).

The ion exchange resin is generally used in a granular size of about0.25 to 1 mm, although particles from 0.15 mm up to about 2 mm may beemployed. The finer catalysts provide high surface area, but also resultin high pressure drops through the reactor. The macroreticular form ofthese catalysts have much larger surface area exposed and limitedswelling which all of these resins undergo in a non-aqueous hydrocarbonmedium compared to the gelular catalysts.

The container employed to hold the catalyst particles may have anyconfiguration, such as the pockets disclosed in the commonly assignedpatents above or the container may be a single cylinder, sphere,doughnut, cube, tube or the like.

Each container containing a solid catalytic material comprises acatalyst component. Each catalyst component is intimately associatedwith a spacing component which is comprised of at least 70 volume % openspace up to about 95 volume open space. This component may be rigid orresilient or a combination thereof. The combination of catalystcomponent and spacing component form the catalytic distillationstructure. The total volume of open space for the catalytic distillationstructure should be at least 10 volume % and preferably at least 20volume % up to about 65 volume %. Thus, desirably the spacing componentor material should comprise about 30 volume % of the catalyticdistillation structure, preferably about 30 volume % to 70 volume %.Resilient materials are preferred. One suitable such material is openmesh knitted stainless wire, known generally as demister wire or anexpanded aluminum. Other resilient components may be similar open meshknitted polymeric filaments of nylon, teflon and the like. Othermaterials such as highly open structures foamed material, e.g.,reticulated polyurethane foam (rigid or resilient) may be formed inplace or applied around the catalyst component.

In the case of larger catalyst components such as from about 1/4 inch to1/2 pellets, spheres, pills and the like, each such larger component maybe individually intimately associated with or surrounded by the spacingcomponent as described above.

It is not essential that the spacing component, entirely cover thecatalyst component. It is only necessary that the spacing componentintimately associated with the catalyst component will act to space thevarious catalyst components away from one another as described above.Thus, the spacing component provides in effect a matrix of substantiallyopen space in which the catalyst components are randomly butsubstantially evenly distributed.

A preferred catalytic distillation structure for use herein comprisesplacing the mole sieve or cation exchange resin particles into aplurality of pockets in a cloth belt, which is supported in thedistillation column reactor by open mesh knitted stainless steel wire bytwisting the two together in a helical form. This allows the requisiteflows and prevents loss of catalyst. The cloth may be any material whichis inert in the reaction. Cotton or linen are useful, but fiber glasscloth or "Teflon" cloth are preferred.

In the following examples the catalyst packing consisted of bags in theform of a fiber glass cloth belt approximately six inches wide withnarrow pockets approximately 3/4 inch wide sewn across the belt. Thepockets are spaced about 1/4 inch apart. These pockets are filled withthe catalyst particles to form approximately cylindrical containers, andthe open ends are then sewn closed to confine the particles. This beltis then twisted into a helical form to fit inside the column. Twisted inwith the belt is also a strip of an open mesh knitted stainless steelwire, which serves to separate the mole sieve filled cloth pockets andprovide a passage for vapor flow.

The wire mesh provides the support for the catalyst (belt) and providessome degree of vapor passage through the catalyst particles, whichotherwise form a very compact bed which has a high pressure drop. Thus,the down flowing liquid is in intimate contact with the rising vapors inthe column.

In commercial-scale operations, it is contemplated, catalyst packingwould be made up of alternating layers of mole sieve filled cloth beltssimilar to the ones described above, and a spacing material which couldbe of any convenient, suitable substance, such as a corrugated wirescreen or wire cloth or a knitted wire mesh. The layers would bearranged vertically or horizontally. For simplicity of fabrication andfor better distribution of vapor flow passages, a vertical orientationis preferred. The height of a section of this packing could be of anyconvenient dimension, from a few inches to several feet. For ease ofassembly and installation, the packing would be made into sections ofthe desired shape and size, each section fastened together withcircumferential bands of tie wires depending on its size and shape. Acomplete assembly in a column would consist of several sections,arranged in layers, with possibly the orientation of the catalyst-filledbelts turned at right angles in successive layers to improve liquid andvapor flow distribution.

The drawing illustrates one species of the present invention, i.e., theproduction ethylbenzene by alkylating benzene with ethylene and apreferred embodiment of that species.

Referring to the drawing distillation column reactor 10 is divided intothree sections. In the middle section the catalyst packing (catalyticdistillation structures) 12 are positioned as described. Linde molecularsieve LZ-Y82 1/16" (Union Carbide Corp.) is deposited in the pockets offiber glass belts and formed in to a helix with stainless steel mesh asdescribed.

The reactor 10 is a four inch diameter pilot column 70 feet tall with 35feet of the catalyst packing in the middle portion. The lower portion ofthe column is a conventional distillation column configuration(equivalent 25 trays). Benzene is conveniently added as makeup via 14into reflux accumulator 16. The benzene can also be added through aseparate line (not shown). The ethylene is fed to the column via 8 atabout the mid point of the catalyst packing 12. The ethylene may also befed at several points to reduce the concentration at any one location inthe catalyst zone, thus reducing oligomerization as a side reaction. Thereaction is exothermic and initiated by contacting the two reactants inthe catalyst packing. Ethyl benzene and diethyl benzene are theprincipal reaction products. Both of these products are higher boilingthan benzene and ethylene and are recovered via 18 as a bottoms product.The feed of ethylene is adjusted such that there is a molar excess ofbenzene in the reactor, such that the overhead 20 is primarily benzene,the ethylene having been almost totally reacted. In addition to benzeneand some ethylene other lights go off overhead. The overhead is passedto condenser 22 which is operated to condense substantially all of thebenzene which passes via 24 to accumulator 16 and hence, by reflux via26 to column 10. The benzene used in the reaction and lost with thelights (which exit condenser 22 via 28) is made up by fresh benzene feed14.

The bottoms contain a mixture of ethyl benzene and diethyl benzene whichpass via 18 to splitter 30, which is a conventional distillation columnoperated to fractionate ethyl benzene and diethyl benzene. The ethylbenzene is recovered as overhead 32 and the diethyl benzene recovered asa bottoms product.

In this preferred embodiment the diethyl benzene is returned to via 34the lower portion of the catalyst packing 12 in column 10, although itcould be recovered as such.

However, in this preferred embodiment it is desired to maximize ethylbenzene production. There is an equilibrium between benzene and diethylbenzene in the catalyst as:

Benzene+Diethyl Benzene→Ethyl Benzene

In the lower portion of the catalyst packing there is substantially noethylene and a large volume of benzene along with the reaction productsand the recycled diethyl benzene, hence, the reversible reaction favorsthe production of ethyl benzene, which is being continuously removedfrom the catalytic zone.

Such conventional items as valves, reboilers, slip streams, etc. are notshown, but would be obvious expedients to those setting up suchequipment.

EXAMPLE 1

The reactor was a 1 inch, six foot stainless tube, composed of 2 footsections bolted together. The bottom and top two feet containedconventional distillation packing, the middle two feet contained molesieve in pockets (four pockets twisted with demister wire) as describedabove. Benzene was fed under nitrogen pressure through a rotometer tothe tower about 6" above the top of the catalyst bed. The olefin, eitherethylene or propylene was fed from a tank pressured with nitrogen to thebottom of the catalyst bed using a micrometering valve. The rate of feedof liquid olefin was adjusted to maintain the tower pressure with slowconstant bleed of gas overhead. The rate of olefin addition was slightlylarger than the rate of reaction.

The benzene feed rate and bottoms withdraw rate are related. The benzenerotometer was set at a given value and the bottom withdrawal rate wasadjusted to maintain a constant bottoms level.

The catalyst was dried initially by taking off some benzene and wateroverhead and an occasional small amount of liquid material was taken offoverhead during runs to maintain the dry catalyst and to remove any lowboiling by-products. Bottoms samples were analyzed by gas liquid phasechromatography using a 50 meter SE-30 capillary column and FID.

The conditions and results of several runs are set forth in TABLE I.

EXAMPLE 2

Using the same reactor as described in EXAMPLE 1, but with Amberlyst 15(acidic cation exchange resin) as the catalyst in the cloth pockets ofthe catalytic distillation structure several runs were carried out toproduce cumene using propylene and ethyl benzene. The conditions andresults are set out in TABLE II.

                                      TABLE I                                     __________________________________________________________________________    RUN NO.      1   2   3   4     5      6    7   8    9    10                   __________________________________________________________________________    Catalyst     Y-82*                                                                             Y-82*                                                                             Y-82*                                                                             SK-500*                                                                             SK-500*                                                                              Y-82*                                                                              Y-82*                                                                             Y-82*                                                                              SK-500*                                                                            SK-500*              Olefin Feed  C3  C3  C3  C3(c) C3(c)  C2   C2  C2   C2   C2                   Pressure, PSIG                                                                             70  75  123 120   120    130  170 220  220  250                  TEMP. F.:                                                                     Bottoms      355 470 540 410   455    475  550 560  440  480                  Lower Cat. Bed                                                                             300 300 341 308   320    343  358 380  340  390                  Upper Cat. Bed                                                                             286 280 330 296   282    325  320 350  294  328                  Recovery Rate                                                                 Overhead     (a) (a) (a) (a)   (a)    (a)  (a) (a)  (a)  (a)                  Bottoms, G./Hr.                                                                            131 165 300 283   Sample 200  38.4                                                                              225  56   93                                                  No Take Off                                    Bottoms Analysis:                                                             Wt. %                                                                         Benzene      73.3                                                                              30.2                                                                              72.5                                                                              62.6  45.2   92.9 65.9                                                                              86.1 93.9 80.7                 Cumene       23.01                                                                             50.4                                                                              25.1                                                                              34.8  50.4   6.7  31.8                                                                              12.5 5.4  16.4                 Dipropyl Benzene                                                                           1.7 13.2                                                                              1.0 1.1   3.4    0.1  1.7 0.7  0.3  1.2                  Polypropyl Benzene                                                                         2.4 3.7 1.1 Trace Trace  0.2  0.5 0.6  0.3  0.6                  Propylene Oligomer                                                                         Trace                                                                             2.5 0.1 1.4   0.9    0.0  0.1 0.1  0.1  0.9                  Production Rate G.                                                            Ethylbenzene/G. Cat. Hr.                                                                   --  --  --  --    --     0.13 0.12                                                                              0.28 0.04 0.22                 Cumene/G. Cat. Hr.                                                                         0.30(b)                                                                           0.83                                                                              0.75                                                                              1.4   --     --   --  --   --   --                   Length of Run, Min.                                                                        39  65  52  18    --     12   50  20   75   55                   __________________________________________________________________________     *Sold By Union Carbide Corp. (Acidic Molecular Sieve)                         (a) Olefin Fed At A Rate To Maintain Pressure With A Slow bleed Overhead.     (b) Catalyst Not Dried Sufficiently.                                          (c) Contained Propylene : Propane = 58/42 Wt. %                          

                  TABLE II                                                        ______________________________________                                        RUN         11         12         13                                          ______________________________________                                        Catalyst    Amberlyst 15                                                                             Amberlyst 15                                                                             Amberlyst 15                                Olefin Feed C.sub.3    C.sub.3    C.sub.3                                     Pressure,   40         20         25                                          PSIG                                                                          Temp °F.                                                               Bottoms     405        335        387                                         Lower Cat.  255        215        228                                         bed                                                                           Upper Cat.  215        215        225                                         bed                                                                           Recovery Rate,                                                                g/hr                                                                          Overhead    (a)        (a)        (a)                                         Bottoms     75         156        106                                         Bottoms Analysis,                                                             Wt. %                                                                         Benzene     27.1       47.1       50.2                                        Cumene      64.2       46.8       45.8                                        Dipropyl    5.0        2.1        0.1                                         Benzene                                                                       Propylene   2.8        3.5        3.1                                         Oligomer                                                                      Production Rate                                                                           0.7        1.0        1.3                                         g. Cumene/                                                                    g. cat./hr.                                                                   Length of Run,                                                                            60         34         52                                          Min.                                                                          ______________________________________                                         (a) Olefin fed at a rate to maintain pressure with a slow bleed overhead 

The invention claimed is:
 1. A process for the alkylation of organicaromatic compounds comprising:(a) concurrently(i) contacting an excessof organic aromatic compound and a C₂ to C₂₀ olefin in a distillationcolumn reactor containing a fixed bed acidic catalytic distillationstructure in a distillation reaction zone thereby catalytically reactingsaid organic aromatic compound and said olefin to form an alkylationproduct and (ii) fractionating the resultant alkylation product and theunreacted organic aromatic compound and olefin in said fixed bed bycontrolling the pressure of said distillation column such that thetemperature within said distillation reaction zone is the substantiallyequal to boiling point of the organic aromatic compound containedtherein, (b) withdrawing said alkylation product from said distillationcolumn reactor at a point below said fixed bed, (c) withdrawing a smallstream of unreacted aromatic compound as overhead and (d) condensingsaid aromatic compound overhead and returning substantially all of saidaromatic compound overhead as reflux.
 2. The process according to claim1 wherein a molar excess of organic aromatic compound to olefin ismaintained in said distillation reaction zone by said reflux ofsubstantially all of said condensed aromatic compound overhead.
 3. Theprocess according to claim 2 wherein from 2 to 100 moles of organicaromatic compound per mole of olefin are present.
 4. The processaccording to claim 3 wherein from 2 to 50 moles of organic aromaticcompound per mole of olefin are present.
 5. The process according toclaim 4 wherein from 2 to 10 moles of organic aromatic compound per moleof olefin are present.
 6. The process according to claim 1 wherein saidorganic aromatic compound has 6 to 20 carbon atoms.
 7. The processaccording to claim 1 wherein said organic aromatic compound has aboiling point of 250° C. or less under the pressure conditions in saiddistillation column reactor.
 8. The process according to claim 1 whereinsaid pressure in said distillation column reactor is in the range of0.25 to 40 atmospheres.
 9. The process according to claim 8 wherein thetemperature is in the range of 80° C. to 500° C.
 10. The processaccording to claim 8 wherein said pressure is in the range of 0.5 to 20atmospheres.
 11. The process according to claim 10 wherein thetemperature is in the range of 80° C. to 300° C.
 12. The processaccording to claim 1 wherein said olefin is a C₂ to C₇ olefin.
 13. Theprocess according to claim 6 wherein said olefin is a C₈ to C₂₀ olefin.14. The process according to claim 6 wherein said organic aromaticcompound is benzene, xylene, toluene, phenol or cresol.
 15. The processaccording to claim 14 wherein said organic aromatic compound is benzene.16. The process according to claim 14 wherein said organic aromaticcompound is phenol.
 17. The process according to claim 14 wherein saidolefin is a C₂ to C₄ olefin.
 18. The process according to claim 15wherein said olefin is ethylene.
 19. The process according to claim 15wherein said olefin is propylene.
 20. The process according to claim 1wherein said acidic catalytic distillation structure is an acidic molesieve catalytic distillation structure.
 21. The process according toclaim 1 wherein said acidic catalytic distillation structure is an acidcation exchange resin catalytic distillation structure.
 22. The processaccording to claim 1 wherein said olefin is fed to said distillationcolumn reactor at a point within said fixed bed.
 23. The processaccording to claim 22 wherein said olefin has a lower boiling point thansaid organic aromatic compound, there being a temperature depression insaid distillation column reactor at a point above the point at whichsaid olefin is fed thereto by the mixture of said organic aromaticcompound and olefin whereby a selected mole ratio of organic aromaticcompound to olefin is maintained by adjusting the moles of olefin feedto maintain the temperature of said temperature depression at apredetermined point.
 24. A process for producing ethyl benzenecomprising:(a) contacting a molar excess of benzene with ethylene in adistillation column reactor containing a fixed bed molecular sievecharacterized as acidic or acidic cation exchange resin catalyticdistillations structure in a distillation reaction zone, at a pressurein the range of 0.25 to 50 atmospheres and temperatures in the range 80°C. to 500° C., thereby concurrently:(i) catalytically reacting saidbenzene and ethylene to form ethyl benzene and diethylbenzene, (ii)fractionating the reaction mixture by controlling the pressure of saiddistillation column such that the temperature within said distillationreaction zone is the substantially equal to boiling point of the benzenecontained therein, (iii) withdrawing ethyl benzene and diethyl benzeneat a point below said fixed bed, and (iv) withdrawing unreacted benzeneat a point above said fixed bed; (b) fractionating said withdrawn ethylbenzene and diethyl benzene; (c) recovering ethyl benzene as a product;(d) Recycling said diethyl benzene to said fixed bed; and (e) returningsaid withdrawn benzene to said distillation column reactor as reflux.25. The process according to claim 24 wherein said ethylene is fed tosaid distillation column reactor at a point within the middle one-halfof said fixed bed and said diethyl benzene recycle is fed at a pointbelow said ethylene.
 26. The process according to claim 25 wherein makeup benzene is added to said reflux.
 27. The process according to claim20 wherein said olefin is a C₂ to C₇ olefin.
 28. The process accordingto claim 27 wherein said organic aromatic compound is benzene, xylene,toluene, phenol or cresol.
 29. The process according to claim 27 whereinsaid organic aromatic compound comprises benzene.
 30. The processaccording to claim 29 wherein said olefin is a mixture of C₂ to C₇olefins.
 31. The process according to claim 29 wherein said olefin isethylene.
 32. The process according to claim 29 wherein said olefin ispropylene.
 33. The process according to claim 21 wherein organicaromatic compound is benzene, xylene, toluene, phenol or cresol.
 34. Theprocess according to claim 33 wherein said organic aromatic compoundcomprises phenol.
 35. The process according to claim 31 wherein saidalkylation product comprises ethyl benzene.
 36. The process according toclaim 35 wherein diethyl benzene is additionally present, and said ethylbenzene is separated and recovered as product.
 37. The process accordingto claim 36 wherein diethyl benzene is contacted with benzene in thepresence of a fixed bed molecular sieve and ethyl benzene produced. 38.The process according to claim 32 wherein said alkylation productcomprises cumene.
 39. The process according to claim 38 wherein dipropylbenzene is additionally present and said cumene is separated andrecovered as product.
 40. The process according to claim 39 wherein saiddipropyl benzene is contacted with benzene in the presence of a fixedbed molecular sieve and cumene is produced.